As the background art in this technical filed, a curved grating, which is an optical element of a spectrophotometer, has both capabilities of spectrally splitting and converging light. Therefore, the number of components can be reduced and the configuration of the device can be simplified.
Conventionally, a curved grating is manufactured by preparing a mold of a diffraction grating by a method in which a curved substrate is carved with a machine such as a ruling engine, and then transferring the carved pattern to a resin, metal or the like.
As a method for preparing a curved grating, WO2008/081555 (PTL 1) discloses a method in which a flat grating and a concave blazed grating are prepared, using semiconductor photolithography and etching processes.
According to JP-A-61-72202 (PTL a diffraction grating pattern is formed on a flexible material such as a resin or thin metal film, which is then attached to a substrate curved to a predetermined curvature, thus forming a mold. This mold is brought in contact with a liquid curved grating material before hardening, and the material is hardened to prepare a curved grating.
According to JP-A-8-29610 (PTL 3), a replica layer (diffraction grating part) using a reactive curing resin is stacked on a flexible substrate, and the flat grating is curved, utilizing the curing contraction of the reactive curing resin.
According to JP-A-9-5509 (PTL 4), a flat grating substrate is transferred to a flexible material such as a silicone resin, which is then fixed to a curved substrate, thus forming a curved grating mold.
JP-A-2010-25723 (PTL 5) discloses an X-ray reflection device having an X-ray reflector which is prepared by heating a silicon substrate to a high temperature in a hydrogen atmosphere so as to plastically deform the silicon substrate into a desired shape, and then stacking a number of the same substrates.